Phonographic device



u Dec. 7, 1948. v H. l.. sHoRTT Al/bert l. J'hrtt Dec. 7, E948. H. 1 sHoRTT PHONOGRAPHIC DEVICE 3 Sheets-Sheet .2

Filed March 15.- 1946 Dec. 7, 1948. H. L. sHoRTT PHONOGRAPH-IC DEVICE 3 Sheets-Sheet 3 Filed March 15, 1946 ma m5 z. L.: .w h n.

Patented Dec. 7, 1948 PHONOGRAPHIC DEVICE,

Hubert L. Shortt, White Plains, N. Y., assgnor to Polytron Corp., White Plains, N. Y., a corporation of New York Application March 15, 1946, Serial No. 654,655

4 Claims.

This invention relates to improvements in phonographic devices, and more specifically to an arm for supporting a phonograph reproducing device wherein the axis of the reproducing device is constantly maintained tangent to the record groove at the point of needle contact, and normal at the same point, to the record radius.

When such a tangency-normality condition obtains, the phonograph reproducer is actuated by the undulations of the record groove, without the introduction of a distortion factor, which would exist if the axis of the reproducer lay at an angle other than 90, with respect to the radially recorded undulations of the record. That this is the case, and that therefore the angular relationship between the reproducer axis and the record groove is of utmost importance for a clear and faithful reproduction, is well known to persons skilled'in the art. For reference, I quote-anarticle by B. B. Bauer, Tracking angle in phonograph pick-ups, in the March 1945` issue` of Electronica page 110.

Several attempts have been made in the prior art to achieve tangency, but satisfactory results have not been obtained hitherto. The principle of devices of the prior art may be understood by means of the following considerations.

Picturing a conventional, single phonograph tone arm, pivoted at one point, it is seen that the reproducer it carries may be tangent to the groove for one, and only, particular value of the radius, that is of the distance from the sylus point to the center of the record, or of the turntable. For all other values of the radius, the reproducer will form an angle with the tangent. The possibility therefore suggests itself that such an angle may be compensated for through controlling cam means of a predetermined prole, in turn controlled by the tone arm, all of the controls requiring arrangements such as pulleys, associated with driving belts, concentric hollow shafts, roller followers. spring connections, and thelike.

Devices of such a type, as well as others involving sliding contacts in conjunction with compensating grooves, roller mechanisms on rails capable of displacing the entire tone arm, and so on, are too cumbersome to handle, too expensive to manufacture, requiring costly precise machining operations, and mechanically unreliable. In general they do not achieve true'tangency. If they get somewhat close to it, it isat the cost of providing structures complicated lbeyond any reasonable limit. Moreover, they `cannot be adapted to operate in conjunction with modern automatic record changers, wherein the reproator of the entire'mechanism, and must be solidly linkedthereto.

Another problem with which this invention is concerned is the distribution of the horizontal frictional force created by the needle drag against the record. The establishment of an equilbrant force to oiset the eiects of this frictional force is a problem quite apart from reproducer tangency considerations, and an improved solution of this problem is an added feature of my invention.

The general object of my invention is to provide a phonograph reproducer supporting device which maintains the axis of the sound reproducer tangent to the record groove and normal to the record radius at the point of needle contact.

Another object is to provide a phonograph reproducer supporting device achieving the above general object, which device is simple, reliable, and easy to manufacture; does not include preformed cams, grooves, or pulley mechanisms and comprises no parts requiring precise machining.

A further object ris to provide such a phonograph reproducer supporting device which is easily adaptable for use in any modern automatic record changing phonograph.

A still further object is to provide means whereby the tangential drag of the needle in the record groove is apportioned among two anchor points.

Other related and ancillary objects Will become apparent as the description proceeds.

My invention will be understood with reference to the appended drawings, wherein:

Fig. 1 is a plan view of a phonograph arm according to my invention, indicating' part' of a frame, a turntable, and a record thereon.

Fig. 2 is a front elevation of the assembly of Fig. 1.

Fig. 3 is a schematic representation ofthe same phonograph arm, wherein various symbols, used in the formulae which occur in the description, are graphically identified.

Fig. 4 is a schematic representation of the same phonograph arm, shown in broken lines in various positions, which together dene the trajectory of the stylus point.

Referring in detail to the drawings, a turntable l of any conventional type is mounted on a suitable frame, of which the supporting board 2, partially shown, is a part, by means of a spindle 3 which is in turn driven by any type of phonograph motor desired. A standard record lis" shown placed. on the turntable I'V forv purpose of the purpose of reproducing the undulations ofV the record groove any type of translating device I0 may be used, such as a standard crystal, a

magnetic, or an electrostatic phonograph pick,- up. The translating device I0 is contained in the receiver section 8 as indi-cated. As'will be shown later, the only mounting requirement is that the axis of the translating device coincide with a line -1 running centrally through the receiver arm 8.y y

One end of a link bars II, of any convenient form, is attached to a point I2 on the receiver arm 8 in any manner which permits a rotational movementwith respect to receiver armV I3. The other end of the link bars I I is pivoted at a point I3 on a rotating member I4 Which-I have chosen to call a link coupler for a very specific reasonj This link coupler, in turn pivoted at I5 to the frame, may have any appearance or shape, artistic or otherwise, so long as pivots I3, I5 and I8 are spaced relative to each other as dictated by the other parameters of this mechanism.

One end of a final lever arm I6 is pivoted at a point II on the driver arm 5, in such a manner as to permit rotational movement with respect to driver arm 5. The other end of arm I6 pivots on the link coupler I4 at a point I8`determined by other parameters of this mechanism. Link bars II and I6 have integral upstanding end projections at pivot points I2 and I'I and integral depending end projections atpivot points I3 and I8, and in connection with such structures I have provided slots in receiver arm 8 and driver arm 5 through which' the upward exten-k sions of the link bars at the respective pivot points pass; likewise I havey provided slots in link coupler I4 into `which depending end projections of link bars yII and I6* pass at their respective pivot points, the extensions of the link bars at the respective pivot point being of suicient length to permit a vertical movement of the driver arm at its pivot 6. It is not essential, however, that all four extensions have relative movement respective to the arms 5 and 8 or the link coupler, it being suflicient that depending extensions I3 and I8'be upwardly movable in relation to link coupler I4 while the extensions at pivot points I2 and I 'I may be connected to the arms 5 and 8 only to provide the requisite lateral movement.

Examining now the described structure as a whole, with reference to the principles of the kinematics of mechanisms, it' is seen that it constitutes a constrained kinematic chain. In fact, it consists of a number of links having pivotal connections each with at least two of the others, which links and connections may -be considered as arranged in a closedvcycle if the supporting frame of the phonograph, which is connected to the driver arm and the link coupler, is looked upon as one of the links, precisely, as the fixed link. The relation between the numberfof links and the number of joints is such vthat the chain is constrained, that is has one degree of freedom, as can be seen by application of the elements of the kinematic theory.

l The property of the chain of being con- 4 strained can -be expressed also by stating that if the position of any link of the chain, chosen as a. driver bar, is fixed, (said driver bar being of course distinct from the fixed supporting frame), then the position of all the other links is also fixed, so that for each position of the driver bar any given point on the chain has one and only one possible position. is equivalent to stating that, if Athe chain is caused to assume all the infinite possible positions of which its structure permits with respect to its fixed supporting frame, any given point of the chain will describe a linear trajectory. In what follows, -I will regard the driver arm 5 as the driving bar` of the chain; and the point I am concerned with is of course the needle point. When the needle rides from the periphery to the center of the record, driver arm 5 rotates clockwise I with respect to its base 1, receiver arm 8 rotates counterclockwise with respect to driver arm 5, and link coupler I4 rotates counterclockwise with respect to the frame about its pivot I5. For my' device to operate the way I want it the needle must then follow a trajectory at every point of which the receiver arm is orthogonal to the record radius. The radial component of the frlctional `force exerted by the needle on the groove then will be substantially eliminated, while at the same time the additional major pivotal point I5 will cooperate with the main pivot 6 to bear the remaining tangential frictional force. l

In practice of course there isno driving force applied to the driver arm. What happens is that the needle point is `guided by the record groove, and follows it. Therefore `it is not necessary to enter into a discussion of the precise geometric type of the groove spiral. The device is adapted to operate with the practical record grooves, and is not limited to any particular spiral equation. l.

In the foregoing, I have made'the statement based on theory, that for each position ofthe driver arm (chosen as driver bar) there is one and only one possible position of each point and link vof my device. Hereafter I will translate this statement into a precise set of mathemati" cal relations, having the purpose better to 4illustrate the operation of the device, and further, to show how the parameters of the device, that is thevarious constant linear dimensions and. oneconstant angle thereof, enter into said operation. Precisely, I will take as my independent variable the angle which the driver arm makes with a certain fixed line, and I will show how the other variable angles and certain variable distances which identify the position of the various links and points of the chain may be expressed as function of the above independent variable only, s'aid functions containing therein thepara'meters of the device. In this manner I will show that, by suitably choosing the parameters of the device, the form of those functions canA be modified at will, which statement means that the trajectory of any chosen point of the chain may be made to conform to operational requirements.

Hereafter, I will refer in detail to Fig. 3. In this figure, the structure of Figs. l and 2 is schematized, representing each link with a straight line, the link coupler being represented with two angularly offset radii. Fixed imaginary lines on the supporting frame are shown in dotand-dash lines, and variable imaginary lines in broken lines. 4The same numerals as in Figs. 1

11:1' sin (1) For mathematical reasons I introduce an imaginary line a, connecting points 9 and 3. Then By definition arm 8 (line D), must be perpendicular to the radius r at point of needle contact, that is, the angle formed by arm 8 and the radius r must be a right angle at all times.

Since C, B, and D are constants, angle is a univocal function of r. That is, for every value of r above the :v axis, there is one and only one value of angle 0.

Likewise, angle qi above the :c axis can have only one value for each Value of angle 0 since it is apparent that sin"1 g 9 By simple trigonometry,

\=cos1 gzgj '(10) Now, angle Z is fixed by the location of point 6 with respect to point 3. Thereforeangle u,

and the angle which makes with the :l: axis is angle We have shown so far that the two basic variables of our spiral Equations 1 and 2 are both functions of angle 0, viz:

=fi(0) by Equation 13 r=f2(0) by Equations 5 and 4 It is now obvious that for every value of radius r and angle above the :l: axis, there can be one and only one value of angle 0, the angle which the driver arm 5 makes with imaginary line (B) drawn between point 6 and 3. In my invention I make very special use of this relation.

We have shown that angle s is, -i109). For physical convenience it has been found necessary to pivot lever I I at a point I2 somewhat removed from the point of needle contact. This creates anew angle 11 with respect to the :l: axis. Weno'w draw imaginary line (y) from point I2 to point 3.

Substitute (13) and (16) in (15), and angle n is remembering that a2=C2+B22BC cos 0, and that C, B, D and H are constants, plus the fact that, 2=a2D2=C2+B2D22BC cos 0 then, v7=f4(0) for given values of C, B, D, and H. That is angle n can have one and only one value for a given value of angle 0.

We now draw imaginary line (f) from point I5 to point l2 and set our equation.

f2=E2 +g2-2Eg eos I, (18) Since g=fs(0), and 1;=f4(0), we have K that is, line (f) can have one and only one value for each value of angle 0, radius 1 remaining above the axis. Moreover, (f) will have a maximum value when angle 0 has a value other than its minimum or maximum. This maximum value of (f) is used to x the total length of radius R' on coupler I4 plus lever arm K or I I.

Any convenient ratio lbetween R and K may be ichosen. In' the illustrated example a ratio of K-R was used to keep the size of the link coupler Id to a small value.

` Angle `f is the angle made by radius R with the Xaxis.

Because f=f5(0) and R and K are constants, Equation 21 is then =f'z(0) If the rotation R is always in the same direc'-V tion as angle 6 moves from maximum to minimum, then angle g can have one and only one value for each value of angle 0. How the rotation of R is kept always in one direction will be shown later. Mathematically, we consider ly positive when R moves above the line (f) andA negative when R moves below the line (f) If we were to consider the starting point of R (as it rotates counterclockwise) to be' that position which it assumes when angle 0 is a minimum, and further consider that radius R is contained in coupler ill, then coupler Ill would be rotated a deiinite number of degrees for each new position of angle 0 as it moves from miniv mum to maximum, or

' assume one and only one value for each value of angleV 9, which in turn means that needle point I9 must follow the trajectory Referring to Figure 3, imaginary line s is drawn from point I5 to point I1. Angle x is a fixed angle formed by line B and line Q. Line W is the distance from point I1 to point 6. Angle ,L is the angle contained between imaginary line Of course Q and W are constants and hence s=f1o(6) because p=f9(0).

The angle which radius L would make with the a: axis is shown as angle a.

Angle T is a xed angle formed at point I5 by line Q and the :r axis. or line E.

and angle o,

or angle o=f11(0) because a=f9(0).

Further, by connecting radius L to arm 5 by means of arm IB or M, we have I Since L and M are constants, and s is a, function of angle by Equation 27, then angle Or, substituting (29), (30), and (31) in (28), we have 2... 2 r=cos1 g--i -2sL-S-B+1*sin1(%sin n) (32) The rotation of link coupler I4 is kept continuous and always in the same direction as angle O moves from maximum to minimum, or vice versa, by setting,

L-I-M=s max (33) The line s will always have a maximum value when angle 0 is minimum.

Further, it will be noted that the dead center points of cranks R, K, and L, M, do not occur at the same time and hence the mechanism cannot lock or change direction for a given movement of the driver arm 5. The angular displacement of points I5 and I8 is determined by the values of angles y and a when line s is maximum and angle o is a minimum, that is, the xed angle between radii R and L is equal to the value of angle s plus angle a when angle 0 is a minimum.

If we consider the starting point of radius L (as it rotates counter clockwise) to be that position which it assumes when angle a is a minimum, and furtherconsider. that radius L is contained in' coupler III,y then coupler I4 will be rotated a definite number of degrees for each new position of angle 0 as angle 0 moves from minimum to maximum, that is.

d www only (34) Now it is obvious that radii R. and L can be contained in coupler I4 if for all values of o. y

Another way of saying the same thing is to consider two rotating radii with a common origin, revolving at the same angular velocity, viz.,

Then. the two radii could be tied together,` and that is exactly What is accomplished by the link coupler I4.

We have now developed a method of rotating coupler I'4 by means of lever I6 for each value of angle o such that receiver arm 8 will be vperpendicular to record radius r for all values of r.

The possible combinations of lever arm lengths, driver and receiver arm lengths, coupler sizes, mounting angles radii to lever arm ratios is beyond discussion here. There are many advantages in selecting regular relationships from a mathematical point of view. Consider Equation 10.

The location of link coupler I4, the selections of points I2 and I1 and the values of arms 5, 8, II, and I6 are mathematically related to each other. There is almost an innite number of combinations of radius L, lever arm M, point I1, and the displacement angle between radius'L and radius R. One or more of these combinations may be used to rotate link coupler I4 as a function of angle 0 such that needle point I9 follows the spiral.

My invention may be considered in eifect a four bar chain. This is easily seen by visualizing the four bars as shown in Figure 3 and remembering that bars s and f have instantaneous values as functions of angle 0.

Apart from the necessity of mounting the reproducer arm 8 to the driver arm 5 so that it pivots at point 9, only three punch press parts are required to modify a standard phonograph supporting arm to a mechanism of .this type, viz., lever arms I6 and II and coupler I4.

It is to be understood that the foregoing description and mathematical discussions have been offered merely by way of illustration and interpretation and that many changes may be made in the arrangement and proportions of my device without departing from the spirit` of the invention or exceeding the scope of the appended claims. l f

I claim: 1. In a phonograph, in combination with a frame a grooved record rotatable on said frame and a stylus-mounting sound reproducing device, wherein said sound reproducing device is mounted on a kinematic chain in such position that at every point of the trajectory of the stylus it mounts said reproducing device tangent to the record groove engaged by said stylus a receiver arm carrying said sound reproducing device, a driver arm pivotally anchored to said frame and pivotally connected to said receiver arm, a link member pivotally anchored to said frame, a rst connecting member pivotally connected to said link member and to said receiver arm at a point intermediate the ends of this latter, and a second connecting member pivotally connected to said link member and to said .driver arm at a point intermediate the ends of this latter.

2. In a phonograph, in combination with a frame carrying a turntable upon which is supported a grooved record and a stylus-mounting sound reproducing device, wherein said sound reproducing device is mounted on a kinematic chain in such position that at every point of the trajectory of the stylus it mounts said reproducing device tangent to the record groove engaged by said stylus a receiver arm carrying said sound reproducing device; a driver arm anchored to the frame so as to swing with respect thereto both in a plane parallel and in a plane perpendicular to the turntable and pivotally connected to said receiver arm; a rst connecting member pivotally connected to said receiver arm at a point intermediate the ends of this latter and pivotally connected to a rst crank arm, this latter being pivotally anchored to the frame; and a second connecting member pivotally connected to said driver arm at a point intermediate the ends of this latter and pivotally connected to a second crank arm, which second crank arm is pivotally anchored to said frame at the same point at which said rst crank arm is anchored; said rst and second crank arm being rigidly connected so that the angle therebetween remains constant; the lengths of the said crank arms, the distances between the pivotal connections of said various aforementioned members, and the distances between the points at which said driver arm and said crank arms are anchored to said frame and the point about which the turntable revolves, being so related that as the stylus moves in the record groove said receiver arm remains perpendicular to the line from the point of the stylus to the center of the turntable.

3. In a phonograph, in combination with a frame a grooved record rotatable on said frame and a stylus-mounting sound reproducing device, wherein said sound reproducing device is mounted on a kinematic chain in such position that at every point of the trajectory of the stylus it mounts said reproducing device tangent to the record groove engaged by said stylus a driver arm pivoted to the frame; a receiver arm pivoted to said driver arm and carrying said sound reproducing device; a link member pivoted to the frame; a first link bar connecting said driver arm and said link member in such a way that when the former is displaced clockwise with respect to the frame the latter is displaced counterclockwise with respect to the frame; and a second link bar connecting said link member and said receiver arm in such a way that when the former is displaced counterclockwise with respect to the frame the latter is displaced counterclockwise with respect to said driver arm, and is thereby maintained tangent to the record groove at the point at which the stylus engages said groove.

4. In a phonograph, in combination with a frame carrying a turntable upon which is supported a grooved record and a stylus-mounting sound reproducing device, wherein said sound reproducing device is mounted on a kinematic chain in such position that at every point of the trajectory of the stylus it mounts said reproducing .device tangent to the record groove engaged by said stylus, a receiver arm carrying said sound reproducing device; a driver arm anchored to the frame so as to swing with respect thereto both in a plane parallel and in a plane perpendicular to the turntable and pivotally connected to said receiver arm; a first connecting member pivotally connected to said receiver arm at a point intermediate the ends of this latter and pivotally connected to a first crank arm, this latter being pivotally anchored to the frame; and a second connecting member pivotally conneeted to said driver arm at a point intermediate the ends of this latter and pivotally connected to a second crank arm, which second crank arm is pivotally anchored to said frame at the same point at which said rst crank arm is anchored; said rst and second crank arm being rigidly connected so that the angle therebetween remains constant; said rst crank arm and first connecting member reaching their dead center relative position when said second crank arm and second connecting member are at an angle to their dead center relative position; the lengths of the said crank arm, the distances between the pivotal connections of said various aforementioned members, and the distances between the points at which said driver arm and said crank arms are anchored to said frame and the point about which the turntable revolves, being so related that as the stylus moves in the record groove said receiver arm remains perpendicular to the line from the point of the stylus to the center of the turntable.

HUBERT L. SHORTT.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,349,636 Swing Aug. 17, 1920 1,885,994 Dieux Nov. 1, 1932 2,025,300 Mueller Dec. 24, 1935 

